Electrical steel sheet provided with coating derived from a carbohydrate and a methylol resin

ABSTRACT

Electrical steel sheet is varnished with a varnish produced by forming an aqueous solution with a pH-value of at least 7 of a carbohydrate having at the most 12 carbon atoms with a resinous product containing methylol groups dissolved in an organic solvent capable of being diluted with water. The carbohydrate may be a monosaccharide, a disaccharide or a hydrolysis product of a disaccharide, starch, sulphite cellulose waste liquor, molasses or the like.

Umted States Patent 1 1 1111 3,865,616 Akerblom 1 Feb. 11, 1975 [541 ELECTRICAL STEEL SHEET PROVIDED 2,427,966 9/1947 Hirschler 260/ 17.5 WITH COATING DERIVED F OM A 2,781,328 2/1957 Ayers 260/172 CARBOHYDRATE AND A METHYLOL 3,313,745 4/1967 Klug 260/175 RESIN o FOREIGN PATENTS OR APPLICATIONS Inventor: Carl-Artur Akerblom, Surahammar, 664,590 1/1952 Great Britain 260/175 Sweden 644,744 4/1937 Germany 260/175 Assigneez Aumanna svenska Elektriska 201,191 1/1966 Sweden 260/175 Aktiebolaget, Vasteras, Sweden I Primary Examiner-Melvin Goldstein [22] Flled' 1972 Assistant Examiner-Edward Woodberry [21] Appl. No.: 305,682

[30] Foreign Application Priority Data [57] ABSTRACT Nov. 22, 1971 Sweden 14889/71 Electrical steel sheet is varnished with a varnish produced by forming an aqueous solution with a pH-value [52] US. Cl. 117/132 BF, 117/161 C, 260/172, of at least 7 of a carbohydrate having at the most 12 260/173, 260/175 carbon atoms with a resinous product containing [51] Int. Cl. C08b 25/00, C08h 15/02 methylol groups dissolved in an organic solvent capa- [58] Field of Search 260/17.2, 17.3, 17.5; ble of being diluted with water. The carbohydrate may 117/132 B, 132 BF, 161 C be a monosaccharide, a disaccharide or a hydrolysis product of a disaccharide, starch, sulphite cellulose [56] References Cited waste liquor, molasses or the like.

UNITED STATES PATENTS 1,209,165 12/1916 Jones 117/161 11 Clams Drawmgs ELECTRICAL STEEL SHEET PROVIDED WITH COATING DERIVED FROM A CARBOHYDRATE AND A METHYLOL RESIN BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to a varnish electrical steel sheet.

2. The Prior Art The properties of the varnish used for varnishing electrical steel sheets are a significant factor in determining the rate of wear of tools employed for punching the sheets. Particularly heavy wear on tools is caused by electrical steel sheets which are coated with a hard varnish, e.g. sheets coated with a heat-treated layer of varnish consisting for the main part of sulphite cellulose waste liquor. Varnishes based on sulphite cellulose waste liquor (for example the varnish described in British Patent Specification No. 664.590) are otherwise well suited for the electrical insulation of electrical steel sheets, since they provide a layerof varnish which adheres well to the sheets and is not damaged during the punching, which would impair the insulation. Consequently, such varnishes are widely used and various methods have been proposed for modifying sulphite cellulose waste liquor in order to avoid its disadvantage of causing considerable wear on punch tools. Up to the present, however, it has been impossible to achieve low wear of the punch tools and at the same time obtain a varnish layer which remains intact during punching.

SUMMARY OF THE INVENTION According to the present invention, however, it has been proved possible to effect varnishes which, when used for varnishing electrical steel sheet, providea sheet having excellent punching properties. When this varnish is used, the result is very little wear on the punch tool and at the same time the varnish layer remains very intact on the piece which is punched out and is not damaged at the edges which are subjected to the influence of the punch tool The layer of varnish formed on an electrical steel sheet coated with the varnish in accordance with the invention has a good electrically insulating resistance, has a very low dusting tendency and causes little gasformation when the sheet is heated. A very important property in the varnish is that it can be applied on the sheet also in very thick layers, such as over microns, which results in the insulation becoming very effective.

Since water can be used to a considerable extent as the solvent in the varnish, manufacture of electrical steel sheet coated with the varnish is simplified, for example the curing of the varnish when it is applied on the sheet.

The present invention thus relates to a varnish for varnishing electrical steel sheet, comprising a binder and a solvent. The varnish is characterised in that the binder at least for the main part comprises a mixture or a partially reacted mixture of a resinous product containing methylol groups and a carbohydrate which at least for the main part comprises a carbohydrate with a carbon chain having at the most 12 carbon atoms.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The resinous product may comprise a product with the capacity to dissolve in a mixture of equal parts by weight of acetone and ethanol and to form a solution containing 50 per cent by weight of the resinous product, which solution is able to be diluted with at least as much water as the quantity of organic solvent without the resin precipitating. This statement as to the properties of the resinous product does not, of course, mean that the resinous product according to the present invention must be used together with the abovementioned solvent used for the characterisation of the resinous product, or in the above-mentioned quantity in the solution. Advantageously the resinous product may consist of a phenolic resin (for example that known under the trade mark LAQVA", Wilhelm Beckers, Stockholm, in which the resinous product is dissolved in a solvent) or of a melamine resin (for ex ample that known under the trade mark CELLA- THERM, Wiesbaden, in which the resinous product is dissolved in a solvent) or of mixtures of phenolic resins and melamine resins (for example that known under the trade mark STOLLACK, Peter Stoll, Vienna, Austria, in which the resinous product is dissolved in a solvent). It is also possible to use, for example, urea resins or mixtures of urea resins with phenolic and/or melamine resins. The mentioned resins may be modified for instance, with alkyds, such as an alkyd substantially built up of glycerol and phthalic acid or with acrylates such as methyl metachrylate.

Examples of carbohydrates which may be used in the manufacture of the varnish are monosaccharides, such as for example pentoses and hexoses, such as .arabinose, xylose, glucose, fructose, mannose and glactose, disaccharides, for example saccharose, maltose, lactose, cellubiose, sorbose, gentiobiose, trehalose and melibiose, polysaccharides, that is saccharides having more than 12 carbon atoms, for example starch and cellulose and also industrial waste products, for example molasses and sulphite cellulose waste liquor, which contain carbohydrates or are composed of carbohydrates which can be liberated by hydrolysis. The carbohydrate may also consist of mixtures of two or more different carbohydrates.

If the carbohydrates consist of long carbon chains such as chains having more than 12 carbon atoms, which is the case with, for example, starch, these are hydrolyzed by treating a highly concentrated acqueous solution of the carbohydrate with acid, for example phosphoric acid, before it is combined with resinous product after a preceding neutralisation with, for example, ammonia or another alkali such as an alkali metal hydroxide or an alkaline earth metal oxide or hydroxide.

If the carbohydrate used is obtained from industrial waste products which, in their production, have been in acid surroundings, or if it consists of carbon chains having at the most l2 carbon atoms, it can be used as it is, in which case it is dissolved in water and the pH of the solution is adjusted when necessary to the desired value, for example with an alkaline phosphate, such as trisodium phosphate, before the resinous product is added. In certain cases, however, it may be advantageous to perform the previously described hydrolysis even of a disaccharide.

The amount of carbohydrate used in the production of the varnish is suitably from 30 to per cent and therefore the amount of the resinous product from 70 to 30 per cent of the total weight of the carbohydrate and the resinous product containing methylol groups.

In many cases it has been found suitable to use the same amount by weight of both components.

In addition to the carbohydrate and the resinous product, the binder may also contain another organic binder, for example, organic substances such as lignin derivatives which are constituents of sulphite cellulose waste liquor.

The varnish may also contain an inorganic and/or organic filler in finely divided form, for example mica powder, clay, an organic polymer, such as polythene, polypropene, polyvinyl chloride in commercial qualities. The filler is suitably used in an amount of from 1 to 30 per cent of the total weight of the non-volatile constituents of the varnish. The particle size of the fillers which may be used is preferably from I to microns. Y

in the manufacture of the varnish an aqueous solution of the carbohydrate, after adjustment of its pH value to at least 7 and preferably-8-l 1, may be mixed with asolution of the resinous product in a solvent which suitably consists at least mainly of an organic solvent capable of mixing with water, for example acetone, ethanol, glycols such as butyldiglycol.

It has been found advantageous to add phosphate groups to the varnish. In this way the adhesion of the varnish to the sheet is improved. Phosphate groups can be added, for example by using phosphoric acid for the hydrolysis-of the carbohydrate used or by using a phosphate when adjusting the pH value of the varnish.

The invention will now be described in greater detail by the following non-limitative Examples.

EXAMPLE l 100 parts by weight of saccharose are dissolved in 100 parts by weight of water and 85 parts by weight of phosphoric acid (s.g. 1.70) is added. After being allowed to stand for 2-6 hours at room temperature the solution is neutralised with ammonia to the pH value 8.

This aqueoussolution is then'mixed with 250 parts by weight of a solution of a phenolic resin or a-melamine resin in an organic solvent (for example the previously mentioned LAQVA or CELL-ATHERM) containing 50 per cent by weight of the phenolic resin or the melamine resin. 5. parts by weight of a wetting agent is also added (for example that known under the trade mark TEEPOOL, Shell, or the trade mark V105, Olof Lindstedt AB, Molndal).

in the varnish obtained by mixing the solution, the carbohydrate content forms about 45 per cent of the total weight of the carbohydrate and resinous product. The varnish is applied on the sheet which is to be insulated, for example by pressure rolling, and is then cured at a temperature of about 300C for 30-60 seconds. The thickness of the layer of varnish, which after penetration is about 3 microns, can be regulated by altering the water content of the varnish.

EXAMPLE 2 A varnish is produced and applied in the manner described in Example 1 except that instead of 100 parts by weight of saccharose 200 parts by weight of molasses is used consisting of 50 per cent by weight of water.

EXAMPLE 3 To 500 parts by weight of evaporated (part of the water removed) sulphite cellulose waste liquor (for example from Katrinefors Paper Mills, which substance consists for the main part of lignin derivatives and carbohydrates) containing 50 per cent by weight of body substance there is added 35 parts by weight of phosphoric acid (s.g. 1.70). When the solution has been treated and neutralised in the manner indicated in Example it is mixed with 200 parts by weight of the resinous solution described in Example 1 and with a wetting agent.

In the finished varnish the total weight of carbohydrate and resinous product comprises more than half the non-volatile constituents of the varnish. Other organic substances deriving from the sulphite cellulose waste liquor, such as lignin derivatives, are also present as components in the binder. The binder thus consists for the main part of carbohydrate and resinous product.

The varnish is applied in the manner indicated in Example l.

EXAMPLE 4 drates) together with 200 parts by weight of water.

In the finished varnish the total weight of carbohydrate and resinous product comprises more than half the non-volatile constituents of the varnish. Other organic substances deriving from sulphite cellulose waste liquor, such as lignin derivatives, are also present as constituents in the binder. The binder thus consists for the main part of the carbohydrate and the resinous product.

a The varnish is applied in the manner described in Example l. I

I 3 EXAMPLE 5 To parts by weight of-starch dissolved in 200 parts by weight of water, there is added 35 parts by weight of phosphoric acid (s.g. 1.70). When the solution has been treated in the manner indicated in Example 1 so that the starch is broken down and neutralised,

it is mixed with 200 parts by weight of the resinous solution described in Example 1 and with a wetting agent. In the finished varnish the carbohydrate content comprises about 50 per cent of the total weight of carbohydrate and resinous product.

The varnish is applied in the manner indicated in Ex ample 1.

EXAMPLE 6 250 parts by weight dried cellulose waste liquor of the type described in Example 4 is dissolved in 200 parts by weight of water and neutralised with 50 parts by weight of trisodium phosphate.

The aqueous solution is mixed with 250 parts by weight of the resinous solution described in Example 1 and mixed with a wetting agent.

in the finished varnish the total weight of carbohydrate and resinous product comprises more than half the non-volatile constituents of the varnish. Other organic substances deriving from the sulphite cellulose waste liquor, such as lignin derivatives, are also present as constituents in the binder. The binder thus consists for the main part of the carbohydrate and resinous product.

The varnish is applied in the manner indicated in Example 1.

EXAMPLE 7 100 parts by weight of saccharose is dissolved in 100 parts by weight of water. The pH value is adjusted to 8 with 30 parts by weight of trisodium phosphate.

This aqueous solution is mixed with the resinous solution described in Example 1 and a wetting agent is added.

In the varnish obtained by mixing the solutions the carbohydrate content comprises about 45 per cent of the total weight of carbohydrate and resinous product.

I claim:

1. An electrical steel sheet provided with a coating derived from a varnish comprising a binder and a solvent, in which the binder consists essentially of a mixture or a partially reacted mixture of a resinous product containing methylol groups and a carbohydrate material consisting essentially of a carbohydrate with a carbon chain having at the most 12 carbon atoms, said resinous product consisting essentially of at least one product selected from the group consisting of phenolic resins, melamine resins and urea resins and having the capacity to dissolve in an organic solvent consisting of a mixture of equal parts by weight of acetone and ethanol to form a solution containing 50 per cent by weight of the resinous product, which solution is capable of being diluted with at least as much water as the quantity of organic solvent without producing precipitation of the resin, in which of the total weight of the carbohydrate and the resinous product containing methylol groups, the weight of the carbohydrate is 30-70 per cent and the weight of the resinous product 70-3O per cent.

2. An electrical steel sheet according to claim 1, in which the carbohydrate consists essentially of a monosaccharide.

3. An electrical steel sheet according to claim 1, in which the carbohydrate consists essentially of a disaccharide.

4. An electrical steel sheet according to claim 1, in which the carbohydrate consists essentially of a hydrolysis product of a substance selected from the group of disaccharides, carbohydrates having more than 12 carbon atoms and products built up of or containing monoor disaccharides or carbohydrates having more than 12 carbon atoms.

5. An electrical steel sheet according to claim 4, in which the carbohydrate consists essentially of a hydrolysis product of starch.

6. An electrical steel sheet according to claim 4, in which the carbohydrate consists essentially of a hydrolysis product of sulphite cellulose waste liquor.

7. An electrical steel sheet according to claim 1, in which the carbohydrate consists essentially of molasses or of a hydrolysis product of molasses.

8. An electrical steel sheet according to claim 1 in which the varnish contains an inorganic filler.

9. An electrical steel sheet according to claim 1, in which the varnish contains an organic filler in the form of finely divided polymer polythene, polypropene or polyvinyl chloride.

10. A method of manufacturing a varnish for an electrical steel sheet according to claim 1, which comprises mixing an aqueous solution of the carbohydrate with a pH-value of at least 7 with the resinous product containing methylol groups dissolved in a solvent which consists essentially of an organic solvent capable of mixing with water.

11. A method of manufacturing a varnish according to claim 10, in which the carbohydrate is formed by hydrolysis of a disaccharide, of a carbohydrate having more than 12 carbon atoms or of a product which is built up of or contains disaccharides or carbohydrates with more than 12 carbon atoms.

* =l l l= 

1. AN ELECTRICAL STEEL SHEET PROVIDED WITH A COATING DERIVED FROM A VARNISH COMPRISING A BINDER AND A SOLVENT, IN WHICH THE BINDER CONSISTS ESSENTIALLY OF A MIXTURE OR A PARTIALLY REACTED MIXTURE OF A RESINOUS PRODUCT CONTAINING METHYLOL GROUPS AND A CARBOHYDRATE MATERIAL CONSISTING ESSENTIALLY OF A CARBOHYDRATE WITH A CARBON CHAIN HAVING AT THE MOST 12 CARBON ATOMS, SAID RESINOUS PRODUCT CONSISTING ESSENTIALLY OF AT LEAST ONE PRODUCT SELECTED FROM THE GROUP CONSISTING OF PHENOLIC RESINS, MELAMINE RESINS AND UREA RESINS AND HAVING THE CAPACITY TO DISSOLVE IN AN ORGANIC SOLVENT CONSISTING OF A MIXTURE OF EQUAL PARTS BY WEIGHT OF ACETONE AND ETHONAL TO FORM A SOLUTION CONTAINING 50 PER CENT BY WEIGHT OF THE RESINOUS PRODUCT, WHICH SOLUTION IS CAPABLE OF BEING DILUTED WITH AT LEAST AS MUCH WATER AS THE QUANTITY OF ORGANIC SOLVENT WITHOUT PRODUCING PRECIPITATION OF THE RESINS, IN WHICH OF THE TOTAL WEIGHT OF THE CARBOHYDRATE AND THE RESINOUS PRODUCT CONTAINING METHYLOL GROUPS, THE WEIGHT OF THE CARBOHYDRATE IS 30-70 PER CENT AND THE WEIGHT OF THE RESINOUS PRODUCT 70-30 PER CENT.
 2. An electrical steel sheet according to claim 1, in which the carbohydrate consists essentially of a monosaccharide.
 3. An electrical steel sheet according to claim 1, in which the carbohydrate consists essentially of a disaccharide.
 4. An electrical steel sheet according to claim 1, in which the carbohydrate consists essentially of a hydrolysis product of a substance selected from the group of disaccharides, carbohydrates having more than 12 carbon atoms and products built up of or containing mono- or disaccharides or carbohydrates having more than 12 carbon atoms.
 5. An electrical steel sheet according to claim 4, in which the carbohydrate consists essentially of a hydrolysis product of starch.
 6. An electrical steel sheet according to claim 4, in which the carbohydrate consists essentially of a hydrolysis product of sulphite cellulose waste liquor.
 7. An electrical steel sheet according to claim 1, in which the carbohydrate consists essentially of molasses or of a hydrolysis product of molasses.
 8. An electrical steel sheet according to claim 1 in which the varnish contains an inorganic filler.
 9. An electrical steel sheet according to claim 1, in which the varnish contains an organic filler in the form of finely divided polymer polythene, polypropene or polyvinyl chloride.
 10. A method of manufacturing a varnish for an electrical steel sheet according to claim 1, which comprises mixing an aqueous solution of the carbohydrate with a pH-value of at least 7 with the resinous product containing methylol groups dissolved in a solvent which consists essentially of an organic solvent capable of mixing with water.
 11. A method of manufacturing a varnish according to claim 10, in which the carbohydrate is formed by hydrolysis of a disaccharide, of a carbohydrate having more than 12 carbon atoms or of a product which is built up of or contains disaccharides or carbohydrates with more than 12 carbon atoms. 